Hot embossing is a micro-structuring process in which a polymer is shaped by heat and pressure using a patterned mold. The main steps are as follows.
1. Heating the Polymer Above Its Glass Transition Temperature
The polymer is first heated above its glass transition temperature. This reduces viscosity and improves flowability during molding. Only above this temperature can the polymer chain segments move sufficiently, allowing the material to enter a highly elastic state and deform quickly under pressure. Excessively high temperature is unnecessary, however, because it lengthens the molding cycle without significantly improving the molded structure. It may also cause warping of the polymer and increase the risk of mold damage.
2. Applying Pressure
Pressure is then applied as the polymer is pressed by the patterned mold. Sufficient pressure is needed to force the polymer into the mold cavities. If the pressure is too low, the cavities cannot be completely filled, and pattern definition will be poor.
3. Cooling Below the Glass Transition Temperature
After molding, the entire stack is cooled to below the glass transition temperature of the polymer. This step solidifies the pattern and provides sufficient mechanical strength before demolding.
4. Demolding
The patterned polymer is separated from the mold. Demolding must be controlled to avoid damaging the fine structures. Mold surface quality and demolding angle are important factors at this stage.
For embossing molds and press plates that require high flatness, precise cavity geometry, or custom alignment features, Hansheng Automation can provide precision machining according to customer drawings to support consistent molding results.
5. Removing the Residual Polymer Layer
After embossing, the recessed areas of the original polymer film remain as an extremely thin residual layer. To expose the substrate surface beneath, this residual layer must be removed. The typical method is anisotropic reactive ion etching, which removes material directionally without significantly attacking the sidewalls of the embossed structures.
6. Pattern Transfer
Pattern transfer can be carried out by two main methods. The first is etching, in which the polymer is used as a mask and the underlying layer is selectively etched to form the desired pattern. The second is lift-off. In the lift-off process, a metal layer, commonly gold, is first deposited over the surface. An organic solvent is then used to dissolve the polymer areas, lifting off the overlying metal together with the polymer. This leaves a metal pattern on the substrate surface. The metal pattern can subsequently be used as a mask for further etching of the layer beneath it.
